The present invention relates generally to an apparatus and a method for patterning a precursor via a pre-conversion step.
The semiconductor and packaging industries, among others, utilize processes to form thin metal and metal oxide films in their products. Conventional processes for forming metal and metal oxide films involve costly equipment and are time consuming. Examples of such processes include evaporation, sputter deposition, thermal oxidation and chemical vapor deposition. Evaporation is a process whereby a material to be deposited is heated near the substrate on which deposition is desired. Normally conducted under vacuum conditions, the material to be deposited volatilizes and subsequently condenses on the substrate, resulting in a blanket, or unpatterned, film of the desired material on the substrate. This method has several disadvantages, including the requirement to heat the desired film material to high temperatures and the need for high vacuum conditions. Unless a screen or shadow is employed during evaporation, an unpatterned, blanket film results from this process.
Sputtering is a technique similar to evaporation, in which the process of transferring the material for deposition into the vapor phase is assisted by bombarding that material with incident atoms of sufficient kinetic energy such that particles of the material are dislodged into the vapor phase and subsequently condense onto the substrate. Sputtering suffers from the same disadvantages as evaporation and, additionally, requires equipment and consumables capable of generating incident particles of sufficient kinetic energy to dislodge particles of the deposition material.
CVD is similar to evaporation and sputtering but further requires that the particles being deposited onto the substrate undergo a chemical reaction during the deposition process in order to form a film on the substrate. While the requirement for a chemical reaction distinguishes CVD from evaporation and sputtering, the CVD method still demands the use of sophisticated equipment and extreme conditions of temperature and pressure during film deposition.
Thermal oxidation also employs extreme conditions of temperature and an oxygen atmosphere. In this technique, a blanket layer of an oxidized film on a substrate is produced by oxidizing an unoxidized layer which had previously been deposited on the substrate.
Several existing film deposition methods may be undertaken under conditions of ambient temperature and pressure, including sol-gel and other spin-on methods. In these methods, a solution containing precursor particles that may be subsequently converted to the desired film composition is applied to the substrate. The application of this solution may be accomplished through spin-coating or spin-casting, where the substrate is rotated around an axis while the solution is dropped onto the middle of the substrate. After such application, the coated substrate is subjected to high temperatures which convert the precursor film into a film of the desired material. Thus, these methods do not allow for direct imaging to form patterns of the amorphous film. Instead, they result in blanket, unpatterned films of the desired material. These methods have less stringent equipment requirements than the vapor-phase methods, but still require the application of extreme temperatures to effect conversion of the deposited film to the desired material.
In one method of patterning blanket films, the blanket film is coated (conventionally by spin coating or other solution-based coating method; or by application of a photosensitive dry film) with a photosensitive coating. This photosensitive layer is selectively exposed to light of a specific wavelength through a mask. The remaining material may also then be used as a pattern transfer medium, or mask, to an etching medium that patterns the film of the desired material or as a circuit or dielectric layer. If used as a mask or etching, then this etch step, the remaining (formerly photosensitive) material is removed, and any by-products generated during the etching process are cleaned away if necessary.
In another method of forming patterned films on a substrate, a photosensitive material may be patterned as described above. Following patterning, a conformal blanket of the desired material may be deposited on top of the patterned (formerly photosensitive) material, and then the substrate with the patterned material and the blanket film of the desired material may be exposed to a treatment that attacks the formerly photosensitive material. This treatment removes the remaining formerly photosensitive material and with it portions of the blanket film of desired material on top. In this fashion a patterned film of the desired material results; no etching step is necessary in this xe2x80x9cliftoffxe2x80x9d process. It is also known that the xe2x80x9cliftoffxe2x80x9d method has severe limitations with regard to the resolution (minimum size) that may be determined by the pattern of the desired material.
In yet another method of forming patterned films, a blanket film of desired material may be deposited, e.g., by one of the methods described above, onto a substrate that has previously been patterned, e.g., by an etching process such as the one described previously. The blanket film is deposited in such a way that its thickness fills in and completely covers the existing pattern in the substrate. A portion of the blanket film is then isotropically removed until the remaining desired material and the top of the previously patterned substrate sit at the same height. Thus, the desired material exists in a pattern embedded in the previously patterned substrate. The isotropic removal of the desired material may be accomplished via an etching process; commonly in the case of the formation of semiconductor devices it is envisioned that this removal is effected through a process known as chemical mechanical planarization (xe2x80x9cCMPxe2x80x9d). This involves the use of a slurry of particles in conjunction with a chemical agent to remove substantial quantities of the desired material through a combination of chemical and mechanical action, leaving behind the desired material in the desired places embedded in the patterned substrate.
While some of these methods are more equipment-intensive than others and differ in the use of either solution- or vapor-phase methods, such conventional processes for forming metal and metal oxide films is not optimal because, for example, they each require costly equipment, are time consuming, require the use of high temperatures to achieve the desired result, and result in blanket, unpatterned films where, if patterning is needed, further patterning steps are required. Many of these methods suffer the additional disadvantage of, in many cases, forming polycrystalline films which may not be suitable for a variety of applications. A desirable alternative to these methods would be the use of a precursor material that may be applied to a substrate and selectively imaged and patterned to form an amorphous film without the need for undesirable intermediate steps.
One use of thin films in semiconductor processing is for the formation of thin top-surface imaging (hereafter xe2x80x9cTSIxe2x80x9d) layers, typically atop organic layers that have already been applied to the substrate. In this instance, the organic layer need not be photoactive, since the thin film to be deposited will be subsequently patterned using conventional methods. The use of these thin films for TSI confers several process advantages, including resistance to plasma etching not afforded by the use of photoresist masks, and the increased resolution of the lithographic process afforded by a very thin film. Typical thin films for TSI include metal and silicon nitride and oxide films, and a great deal of research has also been conducted on a process known as silylation. This process involves the vapor deposition of a thin film of a silicon-containing species on top of a previously deposited organic layer. This thin film of the silicon species can then be imaged to form a thin film of silicon oxide, which acts as the TSI layer during oxygen-plasma patterning of the organic layer beneath. The acceptance of silylation processes by the semiconductor and packaging industries has been insignificant as a result of a number of process and cost limitations.
Another use of thin films in semiconductor processing is for the formation of hard masks, e.g., for use in ion implantation processing. Ion implantation is a well known technique used, for example, in forming doped regions in a substrate during semiconductor fabrication. Ion implantation frequently requires a patterned blocking layer, also known as a hard mask, which directs the ions to be implanted only into predetermined regions. For example, U.S. Pat. No. 5,436,176 to Shimizu et al. discloses, in xe2x80x9cEmbodiment 1xe2x80x9d, maskless implantation of a silicon substrate covered by a silicon oxide film, which is disclosed to be thrice-implanted with boron atoms. Alternatively, the same patent discloses, in xe2x80x9cEmbodiment 3xe2x80x9d, implantation using multiple hard masks in a thrice-repeated method comprising the following sequence of steps: forming a mask on a silicon substrate covered by a silicon oxide film, implantation with phosphorus, forming a second mask, implantation with boron, and, finally, annealing.
As previously discussed, formation of a hard mask by any of these processes requires a relatively large number of process steps. Eliminating some of these steps before etching or ion implantation would be beneficial because, for example, it could simplify the process used, increase its efficiency, and/or reduce its cost.
One approach to solve the problem involves the use of a photoresist as a mask. However, it is well known that photoresists have low etch resistance to certain plasma etching chemistries, particularly for the patterning of organic layers which may be employed as intermediate protecting layers or which are finding increasing use as low-dielectric constant (low-k) dielectrics, and low stopping power for ions. Therefore, undesirably thick photoresist films are required to permit complete etching of the layer to be patterned prior to complete erosion of the masking layer or to prevent implantation of the areas of the substrate onto which they are applied. Another disadvantage is that ion implants and photoresists can be exceedingly difficult to remove from wafers. Other solutions to the problem have been attempted, for example, by first applying a hard mask, then applying a photoresist layer atop the hard mask followed by patterning before etching or ion implantation take place. Combining some of the many steps disclosed in the prior art methods before plasma etching or ion implantation, or even eliminating one or more of them, would help simplify these processes. Thus, a method to eliminate steps in a plasma patterning or an ion implantation process would be highly desirable.
The photochemical processes for metal complex precursor deposition have been developed as less expensive methods of forming amorphous metal and metal oxide patterns. A precursor is at least partially converted to an amorphous metal or metal oxide layer by a partial converting means, e.g., light. As such, the present processes and, specifically, the photochemical metal organic deposition process, has utility in, e.g., the semiconductor and packaging industries.
The processes of the present invention can provide a patterned hard mask, thus replacing both the oxide and photoresist layers used in conventional TSI and ion implantation methods and, for example, simplifying those methods by reducing the number of processing steps which must be performed. Another advantage of this invention is that the material which is produced may have better etch resistance to plasma etching chemistries. This confers still another advantage to the present process that allows for the use of extremely thin films as the hard mask, increasing the ultimate resolution of the lithographic process and allowing the formation of smaller and finer features. A further advantage of this invention is that the material which is produced may have better ion implant blocking and stopping power. Additionally, the process of the present invention is advantageous in that it facilitates the use of new materials for patterned layers, such as platinum, iridium, iridium oxide, ruthenium, ruthenium oxide, and others that are known in the art to be difficult or impossible to etch by conventional processes.
At the current state of photochemical metal organic deposition technology, processing time is an issue. Exposure times are long and become longer as the thickness of the final film of converted precursor increases. Exposure times may reach one hour or more. In order to ensure widespread acceptance of the photochemical metal organic deposition technology, ways of reducing the processing time must be found, developed, and presented to the customers as part of a complete package.
The time required to process a layer of precursor is a barrier to high production efficiency in the photochemical metal organic deposition process. The patterning step in particular is a relatively slow step. What is needed is a way to reduce time required for patterning in the photochemical metal organic deposition process.
The following patents address conventional apparati for, and methods of, transferring wafers, pattern forming, and exposure techniques.
U.S. Pat. No. 5,140,366 describes an exposure apparatus for printing a pattern of a reticle on different shot areas of the wafer in a step-and-repeat manner. In the disclosed apparatus, an image of an alignment mark of the reticle is printed, by use of a projection lens system, on each of some shot areas of the wafer which are selected as the subject of detection. By this, a latent image of the reticle mark is formed on each of the selected shot areas. The latent image of the reticle mark is detected by a microscope which may be a phase contrast microscope and, from the results of detection concerning all the latent images of the reticle mark, a reference (correction) grid representing the coordinate positions of all the shot areas of the wafer is prepared and stored. In accordance with the stored reference grid, the stepwise movement of the wafer is controlled at the time of the step-and-repeat exposures of the wafer. This allegedly improves throughput of the apparatus. Further, use of the phase contrast microscope for the detection of the latent image of the reticle mark ensures further improvement in the alignment accuracy.
U.S. Pat. No. 4,770,590 describes a wafer transfer mechanism used for transferring wafers between cassettes and a boat that uses sensors to detect and to measure any offset of the actual center of each wafer being transferred with respect to the expected or precalibrated center of that wafer. An appropriate adjustment is made to effectively eliminate such offset so that each wafer can be transferred throughout the system without any edge contact between a wafer and the boat or the cassette. The system also includes a boat exchange unit having a rotatable turntable which is used in association with two boats. The boat exchange unit permits a continuous mode operation in which one boat can be undergoing a loading or unloading of wafers at one station on the turntable while another boat is at or is moving to or from a heating chamber loading or unloading station on the turntable.
U.S. Pat. No. 5,534,312 discloses a photoresist-free method for making a patterned, metal-containing material on a substrate which includes the steps of depositing an amorphous film of a metal complex on a surface of a substrate, placing the film in a selected atmosphere, and exposing selected areas of the film to electromagnetic radiation, preferably ultraviolet light and optionally through a mask, to cause the metal complex in the selected areas to undergo a photochemical reaction. However, this reference does not envision use of patterned, metal-containing material as a hard mask to protect underlying layers from a plasma etching environment.
U.S. Pat. No. 5,716,758 describes processes for forming fine patterns on a semiconductor substrate to a lesser degree than the resolving power of a step and repeat, thereby improving the degree of integration of the semiconductor device. The process comprises the steps of: forming a first light-exposure mask and a second light-exposure mask with interlaced patterns selected from a plurality of fine patterns to be formed on a semiconductor substrate; coating an organic material layer on the semiconductor substrate; patterning the organic material layer by use of the first light-exposure mask, to form organic material layer patterns; forming a photosensitive film over the organic material layer patterns; and patterning the photosensitive film by use of the second light-exposure mask to form photosensitive film patterns, in such a way that each of photosensitive film patterns is interposed between two adjacent organic material layer patterns.
U.S. Pat. No. 5,935,762 describes a new method for forming dual damascene patterns using a silylation process. A substrate is provided with a tri-layer of insulation formed thereon. A first layer of silylation photoresist is formed on the substrate and is imaged with a hole pattern by exposure through a mask. Using a silylation process, which greatly improves the depth of focus by reducing reflections from the underlying substrate, the regions in the first photoresist adjacent to the hole pattern are affixed to form top surface imaging mask. The hole pattern is then etched in the first photoresist. A second layer of photoresist is formed, and is imaged with a line pattern aligned with the previous hole pattern by exposure through a mask. The line pattern in the second photoresist is etched. The hole pattern in the first photoresist is transferred into the top layer of composite insulation first and then into the middle etch-stop layer by successive etching. The line pattern in the second photoresist layer is transferred into the first photoresist layer through a subsequent resist dry etching process. Finally, the line pattern and the hole pattern are transferred simultaneously into the top and lower layers of the composite insulation layer, respectively, through a final dry oxide etching. Having thus formed the integral hole and line patterns into the insulation layer, metal is deposited into the dual damascene pattern. Any excess metal on the surface of the insulating layer is then removed by any number of ways including chemical-mechanical polishing, thereby planarizing the surface and readying it for the next semiconductor process.
U.S. Pat. No. 5,989,759 describes a method where in the case of forming a fine pattern by exposure after exposure of a rough pattern, the exposure position of the rough pattern is adjusted, based on a latent image of the rough pattern, which has been subjected to exposure. As a result, a positional displacement between rough and fine patterns is reduced so that a desired pattern can be formed with high accuracy. To achieve down-sizing and improvements of throughputs, light exposure and charge beam exposure are sometimes used together. In case of performing exposure of a desired pattern in a plurality of stages, a positional displacement of each of exposure patterns in the stages leads to a decrease in exposure accuracy.
The present invention relates to a method of converting an organometallic precursor material to a metal-containing pattern adherent to a substrate, comprising: applying the organometallic precursor material in an amount sufficient to coat at least a portion of the substrate, wherein said organometallic precursor material is adapted to be converted to form a metal or metal oxide; pre-converting the organometallic precursor material by exposing the organometallic precursor material to a pre-conversion energy exposure dose such that the pre-converted precursor material is not converted to a degree sufficient to impair pattern resolution; pattern converting a portion of the pre-converted precursor material to convert this portion to a pattern-converted material to an extent sufficient to thereby form a pattern on the substrate; and either:
1) developing the portion of the pre-converted precursor material that was not pattern-converted such that the pattern remains on the substrate after developing; or alternately,
2) pattern converting a second portion of the pre-converted precursor material to convert this portion to a pattern-converted material an extent sufficient to thereby form a second pattern on the substrate; and developing the second portion of the pre-converted precursor material that was pattern-converted such that the second pattern remains on the substrate after developing.
In one embodiment, the pattern conversion comprises exposing the pre-converted precursor material to a patterning energy exposure dose, which converts the pre-converted precursor material to metal or metal oxide that adheres to the substrate to an extent sufficient to thereby form a deposited pattern thereon.
In another embodiment, the pre-conversion energy exposure dose is selected to be about 20% or less of, alternately from about 20% to about 50% of, the combination of the pre-conversion energy exposure dose and the patterning energy exposure dose, such that the pre-converted precursor material is substantially developable.
In yet another embodiment, the pre-conversion, the pattern-conversion, or both, comprises photochemical metal organic deposition. In still another embodiment, the pre-conversion comprises forming a metal or metal oxide within the organometallic precursor material.
In yet another embodiment, the pre-conversion energy exposure dose is selected to be from about 30% to about 80%, alternately from about 60% to about 99%, alternately about 50% or more, of a maximum pre-conversion energy exposure dose, wherein the maximum pre-conversion energy exposure dose is that energy dose above which the organometallic precursor material exposed to the pre-conversion energy exposure dose is no longer substantially developable or above which the organometallic precursor material exposed to the pre-conversion energy exposure dose adheres to the substrate to a degree sufficient to impair pattern resolution, wherein the organometallic precursor material exposed to the pre-conversion energy exposure dose is substantially developable.
The invention also relates to a substrate containing a patterned metal or metal oxide layer formed according to the invention.
In another embodiment, the pre-conversion comprises exposing the precursor material to a heat source, and wherein the pattern-conversion comprises exposing the pre-converted precursor material to a light source. In yet another embodiment, the pre-conversion comprises exposing the precursor material to a heat source, and wherein the pattern-conversion comprises exposing the pre-converted precursor material to an electron-beam source. In still another embodiment, the pre-conversion comprises exposing the precursor material to an electron-beam source, and wherein the pattern-conversion comprises exposing the pre-converted precursor material to a light source. In yet another embodiment, the pre-conversion comprises exposing the precursor material to a light source, and wherein the pattern-conversion comprises exposing the pre-converted precursor material to a light source.
The invention also relates to an apparatus for converting an organometallic precursor material to a metal-containing film adherent to a substrate formed by a method according to the above-described methods, comprising: a load station to store the substrate before processing; a means of delivering the substrate between processing steps; a pre-convert section, wherein the substrate is coated, if previously uncoated, with a sufficient amount of the organometallic precursor material and is subjected to a first converting means in either a series or parallel arrangement; a pattern convert section, wherein the organometallic precursor material coated on the substrate, subjected to a first converting means, and not covered by a mask is substantially converted, using a second converting means, to form a metal-containing pattern adherent to the substrate; and an unload station where the pattern-coated substrate is stored after processing. Advantageously, the first and second converting means are the same or different, and wherein each comprises a heat source, a light source, a coherent light source, a broadband light source, an electron beam source, or an ion beam source.
The invention also relates to a method of selecting a pre-conversion energy exposure dose and a patterning energy exposure dose to be used in converting an organometallic precursor material to a metal-containing patterned layer comprising at least two pattern elements that are adherent to a substrate, which method comprises: determining a relationship between the pre-conversion energy exposure dose in the conversion and the amount of pre-converted precursor material that adheres to the substrate; and selecting a pre-conversion energy exposure dose that is less than a maximum pre-conversion energy exposure dose, wherein the maximum pre-conversion energy exposure dose is that energy dose above which the organometallic precursor material exposed to the pre-conversion energy exposure dose is no longer substantially developable or above which the organometallic precursor material exposed to the pre-conversion energy exposure dose adheres to the substrate to a degree sufficient to impair pattern resolution, such that the patterning energy exposure dose yields an acceptable pattern resolution on the substrate, wherein the acceptable pattern resolution is such that the at least two elements of the metal-containing patterned layer are discrete and not connected by like material.
Advantageously, the method can further comprise identifying a maximum pre-conversion energy exposure dose based on the dose-conversion relationship, such that the organometallic precursor material exposed to the pre-conversion energy exposure dose, but not to the patterning energy exposure dose is substantially removable during developing. In one embodiment, the pre-conversion energy exposure dose is selected to be about 20% or less, or alternately from about 20% to about 50%, of the combination of the pre-conversion energy exposure dose and the patterning energy exposure dose, such that the pre-converted precursor material is substantially developable.
In another embodiment, the pre-conversion energy exposure dose is selected to be from about 30% to about 80%, alternately from about 60% to about 99%, alternately about 50% or more, of a maximum pre-conversion energy exposure dose, wherein the maximum pre-conversion energy exposure dose is that energy dose above which the organometallic precursor material exposed to the pre-conversion energy exposure dose is no longer substantially developable or above which the organometallic precursor material exposed to the pre-conversion energy exposure dose adheres to the substrate to a degree sufficient to impair pattern resolution, wherein the organometallic precursor material exposed to the pre-conversion energy exposure dose is substantially developable.